List Merge (List L1,List L2){
    List p = L1->Next;
    List q = L2->Next;
    List L = (List )malloc(sizeof(PtrToNode));
    L->Next = NULL;
    List r = L->Next;//r是L的终端节点
    free(L2);
    free(L1);
    while (p!=NULL &&q!=NULL){
        if (p->Data<=q->Data){
            r->Next = p;
            p = p->Next;
            r = r->Next;
            L1->Next = NULL;
            L2->Next = NULL;
        }
        else {
            r->Next = q;
            q= q->Next;
            r= r->Next;
            L1->Next = NULL;
            L2->Next = NULL;
        }
    }
    r->Next=NULL;
    if (p!=NULL){
        r->Next= p;
        return L;
    }
    if (q!=NULL){
        r->Next = q;
        return L;
    }
    return L;
}